Detail of GB 20840.2-2014

Introduction of GB 20840.2-2014

1 Scope This part of GB 20840 is applicable to newly manufactured inductive current transformers for use with electrical measuring instruments and/or electrical protective devices having rated frequencies from 15Hz to 100Hz. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Clause 2 of GB 20840.1-2010 is applicable with the following additions: GB/T 156 Standard voltages (GB/T 156-2007, IEC 60038:2002, MOD) GB 311.1 Insulation co-ordination - Part 1: Definitions, principles and rules (GB 311.1-2012, IEC 60071-1:2006, MOD) GB/T 3954 Aluminium and aluminium alloys rod for electrical purpose GB/T 5585.1 Copper or aluminium and its alloy bus bars for electrical purposes - Part 1: Copper and copper alloy bus bars GB/T 7252 Guide to the analysis and the diagnosis of gases dissolved in transformer oil (GB/T 7252-2001, IEC 60599:1999, NEQ) GB/T 7595 Quality of transformer oils in service GB 20840.1-2010 Instrument transformers - Part 1: General requirements (IEC 61869-1:2007, MOD) 3 Terms and definitions For the purposes of this document, the terms and definitions in GB 20840.1-2010 apply with the following additions: 3.1 General definitions 3.1.201 current transformer instrument transformer in which the secondary current, under normal conditions of use, is substantially proportional to the primary current and differs in phase from it by an angle which is approximately zero for an appropriate direction of the connections [GB/T 2900.15-1997, definition 3.4.5] 3.1.202 measuring current transformer current transformer intended to transmit an information signal to measuring instruments and meters [GB/T 2900.15-1997, definition 3.4.8, modified] 3.1.203 protective current transformer a current transformer intended to transmit an information signal to protective and control devices [GB/T 2900.15-1997, definition 3.4.7, modified] 3.1.204 class P protective current transformer protective current transformer without remanent flux limit, for which the saturation behaviour in the case of a symmetrical short circuit is specified 3.1.205 class PR protective current transformer protective current transformer with remanent flux limit, for which the saturation behaviour in the case of a symmetrical short circuit is specified 3.1.206 class PX protective current transformer protective current transformer of low-leakage reactance without remanent flux limit for which knowledge of the secondary excitation characteristic and of the secondary winding resistance, secondary burden resistance and turns ratio, is sufficient to assess its performance in relation to the protective relay system with which it is to be used 3.1.207 class PXR protective current transformer protective current transformer with remanent flux limit for which knowledge of the excitation characteristic and of the secondary winding resistance, secondary burden resistance and turns ratio, is sufficient to assess its performance in relation to the protective relay system with which it is to be used Note 201: An increasingly number of situations occurs where direct current components are continuously flowing through current transformers. Therefore, in order to stop the current transformer from saturating, current transformers with air gaps, but with the same performance as class PX, are used. Note 202: The air gaps for remanence reduction do not necessarily lead to a high-leakage reactance current transformer (see Annex 2C).

Contents of GB 20840.2-2014

Foreword i Introduction iv 1 Scope 2 Normative references 3 Terms and definitions 3.1 General definitions 3.3 Definitions related to current ratings 3.4 Definitions related to accuracy 3.7 Index of abbreviations 5 Ratings 5.2 Highest voltage for equipment 5.3 Rated insulation levels 5.5 Rated output 5.6 Rated accuracy class 5.201 Standard values for rated primary current 5.202 Standard values for rated secondary current 5.203 Standard values for rated continuous thermal current 5.204 Short-time current ratings 6 Design and construction 6.4 Requirements for temperature rise of parts and components 6.5 Grounding requirements of equipment 6.13 Markings 6.201 Requirements for insulating oil performance 6.202 Requirements for outlet terminal 6.203 Structural requirements for oil-immersed current transformer 7 Test 7.1 General 7.2 Type tests 7.3 Routine test 7.4 Special tests 7.5 Sample tests Annex 2A (Informative) Structural changes of this part with respect to IEC 61869-2:2012 Annex 2B (Informative) Technical changes and reasons between this part and IEC 61869-2:2012 Annex 2C (Normative) Verification of low leakage reactance current transformer Annex 2D (Normative) Protective current transformers classes P, PR 2D.1 Vector diagram 2D.2 Turns correction 2D.3 The error triangle 2D.4 Composite error 2D.5 Direct test for composite error 2D.6 Alternative method for the direct measurement of composite error 2D.7 Use of composite error Annex 2E (Normative) Protective current transformer classes for transient performance 2E.1 Basic theoretical formulas for transient dimensioning 2E.2 Measurement of the core magnetization characteristic 2E.3 Direct test for determination of the error at limiting conditions Annex 2F (Informative) Method used in temperature rise test of oil-immersed transformers to determine the thermal constant by an experimental estimation Annex 2G (Informative) Alternative measurement of the ratio error (ε) Annex 2H (Normative) Determination of the turns ratio error